Date of Award

Summer 2010


© 2010 Joseph Sungail

Document Type


Degree Name

Master of Science in Marine Sciences


Marine Science

First Advisor

Anne Christine Brown

Second Advisor

Stephan Zeeman

Third Advisor

Kathryn A. Ono


The intertidal zone in the Gulf of Maine supports large populations of three species of decapods. Young green crabs (Carcinus maenas), rock crabs (Cancer irroratus) and American lobsters (Homarus americanus) co-exist in close proximity and forage on similar prey species. Competition for prey resources could have major implications for the populations of these predators. This experimental study focuses on determining the potential for interspecific competition between these decapods for prey resources. Young green crabs (25 - 35 mm carapace width), rock crabs (25 - 35 mm carapace width) and American lobsters (25 - 35 mm carapace length), were collected along with the prey species blue mussels (Mytilus sp.), rock barnacles (Semibalanus balanoides) and common southern kelp (Saccharina latissima) from the intertidal of the southern section of Saco Bay in the Gulf of Maine. Claw measurements were taken, prey size and prey species preference was tested and caloric value of prey was determined. Morphological measurements indicated that all three decapod species had different sized chela relative to body size. The three predators preferred similar sized mussels and barnacles, and had similar handling times for both of these prey species. None of the three predator species consumed measurable amounts of kelp. Rock crabs and lobsters preferentially selected mussels over barnacles, while green crabs consumed equal amounts of both prey species. The preferred mussel size was smaller than the calculated optimum while the optimal barnacle size was eaten. These results suggest that while green crabs, rock crabs and lobsters have differing claw morphologies, they select similar prey and consume prey at the same rate. Therefore there is a possibility of intense interspecific competition among these predators.


Master's thesis.

This thesis is related to the article "Prey selection by Gulf of Maine green crabs (Carcinus maenas), rock crabs (Cancer irroratus) and American lobsters (Homarus americanus): A laboratory study," published November 2013 in the Journal of Experimental Marine Biology and Ecology: